The plasma surface processing apparatus is provided with a pair of electrodes (for example, Japanese Patent Application Laid-Open No. H11-236676). A processing gas is introduced between the pair of electrodes and an electric field is also impressed therebetween to generate a glow discharge. By this, the processing gas is plasmatized. The processing gas thus plasmatized is blown to the surface of a base material of a semiconductor base material or the like. By this, such processing as film formation (CVD), etching, ashing, cleaning and surface modification can be conducted with respect to the surface of the base material.
The number of electrodes provided to a single apparatus is not limited to two. For example, in a plasma processing apparatus disclosed in Japanese Patent Application Laid-Open No. H05-226258, a plurality of electrodes are arranged such that their polarities are alternately appeared.
A plasma surface processing system includes a so-called direct system in which a base material is disposed in an electric field impressing space between a pair of electrodes, and a so-called remote type in which a base material is disposed away from an electric field impressing space and a processing gas plasmatized in the electric field impressing space is blown to this base material. It further includes a low pressure plasma processing system in which the entire system is put into a pressure reducing chamber and processing is conducted in a lower pressure circumstance, and a normal pressure processing system in which processing is conducted under pressure (generally normal pressure) close to atmospheric pressure.
For example, as disclosed in Japanese Patent Application Laid-Open No. H11-251304, the remote type normal pressure surface processing apparatus comprises a blowoff nozzle for blowing out a processing gas. Within this nozzle, a pair of electrodes are arranged in opposing relation. At least one of the electrodes is provided at an opposing surface thereof with a solid dielectric layer such as ceramic by thermally sprayed coating film. This arrangement is made in order to prevent the occurrence of arc discharge occurrable in a normal pressure interelectrode space. The nozzle is formed with a blowoff passage which is continuous with the electric field impressing space between the electrodes. The base material is disposed ahead of this blowoff passage.
The gas to be used for plasma surface processing is selected depending on the purpose of processing. In case of film formation (CVD), gas containing the raw material of film is used. This raw material gas is introduced between the electrodes and reacted with plasma to form a film on the surface of a base material.
However, this film formation processing technique has such a problem that the film, which is originally intended to be adhered to the base material, is liable to adhere to the apparatus side. Particularly, in the remote type, the gas is readily adhered to the surface of the electrode before it is blown off from the blowoff passage. The gas is also readily adhered to the peripheral area of the blowoff passage of the nozzle or to the opposing surface of the nozzle with respect to the base material. This results in loss of an increased amount of raw material. Maintenance such as replacement of electrodes, etc. and cleaning thereof is more frequently required. Total replacement of the main component such as electrodes means significant waste of the component materials. Moreover, it is extremely troublesome to totally clean the nozzle in order to remove the adhesion (stain) adhered to the peripheral area of the blowoff passage. In addition, the processing must be temporarily stopped during the maintenance.
Incidentally, Japanese Patent Application Laid-Open No. H03-248415 discloses a technique in which in the normal pressure CVD, in general, the wall surface from the peripheral area of the nozzle to its discharge part is composed of a wire netting and an inert gas is blown off through the meshes of the wire netting, thereby to prevent the film from adhering to the apparatus side. This techniques, however, again has such a problem that the flow of processing gas is disturbed by the inert gas coming through the meshes, thus badly degrading the film formation efficiency onto the base material.
Moreover, the normal pressure plasma surface processing has such a problem that an average free travel (life span) of the radicals is short compared with the lower pressure circumstance. For this reason, if the nozzle is arranged too away from the base material, it becomes unable to form a film due to deactivation. On the other hand, if the nozzle is arranged too close to the base material, arc is liable to occur between the electrode on the side to which the electric field is impressed and the base material, and the base material gets, in some instances, damaged.
In the normal pressure plasma surface processing, arc (abnormal electric discharge) may occur at the rear surface (reversed side surface of the opposing surface) of the electrode and at the edge of the electrode. This occurs particularly significantly when rare gas including argon or hydrogen is used as processing gas.
The present invention has been made in view of the above situation. It is, therefore, an object of the present invention to provide a technique for solving the problem of film adhesion to the electrodes, etc., at the time of plasma film formation, particularly at the time of plasma film formation according to the remote type, of all the plasma surface processing. It is another object of the present invention to provide a technique capable of conducting a favorable film formation processing while preventing the arc discharge.